Produce Rouse sarcoma virus, Prague "C" strain on a continuing but flexible basis at a level of 100 liters of virus-containing tissue culture fluid per week. The Rous sarcoma virus will be produced in the chick embryo fibroblast or equivalent tissue culture system with varying times of harvest and methods of processing tissue culture fluids to obtain Rous sarcoma virus that would favor the subsequent isolation of either structural proteins, high molecular weight viral RNA, or viral glycoproteins. In addition, other strains of the Rous sarcoma virus or other species of avian tumor viruses may be substituted by the NCI Project Officer to the extent necessary to accomodate changes in the research thrust of the scientific community.